1. FIELD OF THE INVENTION
This invention relates to improved wood fibrous materials and a method for improving the same which imparts dimensional stability to them.
2. DESCRIPTION OF THE PRIOR ART
Wood fibrous materials, including, for example, woods, processed woods, (hereinafter both are called woods), paper and processed paper have peculiar advantages in that they are easily obtainable, the processing thereof is simple, and they are light in weight, high in strength, low in thermal conductivity, low in specific heat and excellent in acoustic-and mechanical oscillating-absorptivity.
On the other hand, they have disadvantages in that they absorb water or get wet so that they swell, and when they are dried, they discharge the water contained therein so that they shrink, with the result being that they crack, deform and warp and also they are low in strength and their electric properties are degraded when they get wet or absorb water.
Heretofor, for the purpose of stabilizing wood fibrous materials against shrinking and swelling, which occur due to their hygroscopicity, and preventing deterioration of their other properties, methods for improving the qualities of the wood fibrous materials have been adopted comprising using polyethylene glycol (hereinafter called PEG) of a molecular weight of 200 to 4000 or using vinyl series monomers such as styrene, methyl methacrylate, 2-hydroxyethyl methacrylate and the like.
However, the method of using PEG has disadvantages in that when PEG having a molecular weight of from 200 to 1000 is used, the impregnation rate is rather high but the treated wood fibrous material is high in hygroscopicity and when PEG having a molecular weight of more than 1000 is used, the resulting wood fibrous materials are preferable in hygroscopicity but the impregnation rate of the PEG is low, with the result being that they are not sufficiently stabilized against swelling and shrinking and, moreover, a secondary procedure of cross-linking or curing by a diisocyanate or formaldehyde must be carried out for preventing elution of the PEG with the passage of time and the treated wood fibrous materials become generally low in the strength.
Further, the method of using hydrophobic vinyl monomers such as styrene, methyl methacrylate and the like, can not sufficiently stabilize the treated fibrous materials against swelling and shrinking and they become cracked with the passage of time and even if they are increased in density, or plasticized, or become harder, after the impregnation procedure, they lose their special property of impact strength.